Hydraulic gimbal lock

ABSTRACT

An improved lock is disclosed, as applied to the elevation gimbal of a large telescope installation. Hydraulic pressure is employed firmly and simultaneously to force a number of contact members against a stationary surface of circular configuration and forming part of the fork gimbal or yoke pedestal. The hydraulic pressure is made effective by the use of a bellows system in which each bellows carries a contact head positioned a short distance from the stationary surface and the bellows are equally spaced from one another. A solenoid having a movable core and controlled from a position near the eyepiece of the telescope is employed to operate a miniature hydraulic pump which feeds oil under pressure simultaneously to each of the bellows. The latter elongate and press firmly against the stationary surface and at the same time, the motor which drives the gimbal to which the telescope is attached, can be declutched so that instant braking is effected. There is no overrun and the telescope remains strictly in line with the star being sighted when the control is operated.

United States Patent 72] Inventors Moshe L. Plawner Wayne; Vincent R.Vento, Morris Plains; Abraham Gordon, Teaneck, NJ. [2]] Appl. No.878,116 [22] Filed Nov. 19, 1969 [45] Patented May 25, 1971 [73]Assignee The United States of America as represented by the Secretary ofthe United States Air Force [54] HYDRAULIC GIMBAL LOCK 8 Claims, 7Drawing Figs.

[52] U.S. Cl 188/74, 350/83 [51] 1nt.Cl F16d 51/00 [50] Field of Search350/82, 83, 85; 188/74, 184 356/(Inquired) [5 6] References Cited UNITEDSTATES PATENTS 2,326,552 8/1943 Morse 350/83 3,338,350 8/1967 SchillingABSTRACT: An improved lock is disclosed, as applied to the elevationgimbal of a large telescope installation. Hydraulic pressure is employedfirmly and simultaneously to force a number of contact members against astationary surface of circular configuration and forming part of thefork gimbal or yoke pedestal. The hydraulic pressure is made effectiveby the use of a bellows system in which each bellows carries a contacthead positioned a short distance from the stationary surface and thebellows are equally spaced from one another. A solenoid having a movablecore and controlled from a position near the eyepiece of the telescopeis employed to operate a miniature hydraulic pump which feeds oil underpressure simultaneously to each of the bellows. The latter elongate andpress firmly against the stationary surface and at the same time, themotor which drives the gimbal to which the telescope is attached, can bedeclutched so that instant braking is effected. There is no overrun andthe telescope remains strictly in line with the star being sighted whenthe control is operated.

PATENTEU HAY25 IHYI SHEET 1 [IF 3 SHEET 2 OF 3 PATENTED HAY25 l9?!HYDRAULIC GIMBAL LOCK BACKGROUND OF THE INVENTION Large telescopeinstallations are employed for sighting distant stars, trackingsatellites, also for observing the travel of space vehicles and theoperation of propulsion rockets, etc. Many of these telescopes arehoused in observatories and most of them are operated by electric motorsthrough pushbutton control, operated by the observer at the eyepieceposition. The telescope proper is usually fixedly mounted on at leastone four-sided gimbal carried on trunnions and the gimbal is swingablebetween the legs of an upright fork structure or yoke. The latter isprovided with a heavy central column, swingable or rotatable in avertical bearing. For convenience the last-mentioned structure will betermed a fork gimbal to distinguish it from the quadrilateral gimbal onwhich the telescope proper is mounted. Both gimbals are quite massiveand usually have square cross sections of wide and thick dimensionswitha hollow interior so as to reduce the weight as much as possible. Thetelescope is fixedlymounted on the quadrilateral gimbal and the latteris adapted to swing within the space between the two opposite legs ofthe yoke or fork structure. Thus, the telescope can be swung in thevertical direction with its gimbal and in the horizontal or azimuthdirection by the turning movement of the fork gimbal in its bearing.

While great effort is made to balance the quadrilateral gimbal carryingthe telescope about its bearing in an attempt to make it swingable byhand, at the larger installations it has been found more practical tomotor drive both gimbals under the control of the observer. However, ithas been found that notwithstanding the care taken by the latter, eitherto power drive or hand operate the gimbals in order to quickly give thetelescope the proper orientation, the gimbals tend to overrun andsometimes to underrun the proper position so that a back and forthshifting movement may become necessary. Even microservomechanism andslow gearing are not always sufficient to prevent the occurrence of anundesired movement of the heavy parts which have considerable momentumeven when being moved slowly. Sometimes a fast fix on a star becomes anabsolute necessity in which the parts must be moved rapidly and in thatcase the problem of wobble about the proper position could becomeaggravated. Various attempts have been made to devise fast stoppage ofthe moving parts on command and perhaps the most recent was the use of amechanical wedge which was jammed between two machined surfaces of thegimbals. In addition to the difficulty of quickly removing the wedge,the lock operated erratically and occasionally jammed in the lockedposition. This is particularly so if the support on which the telescopeis mounted is subject to vibration from an extraneous source such as arocket in the propulsion stage. Moreover, the wedge form of lock becomesalmost impossible when it is necessary to quickly unlock the trunnionsand orient the telescope on a second star in which the switchingoperation, including the unlock and subsequent lock action, must be keptwithin a matter of a few seconds.

SUMMARY OF THE INVENTION An object of the invention is to provide atelescope mount 'part of the mount.

Another object is toprovide a device or structure which is applicable totelescopes employing heavy swingable mounts and which will prevent eventhe slightest overrun beyond the desired predetermined swingingmovement.

Still another object is to provide an improved device or structure forlocking the elevation gimbal and the yoke gimbal together at the exactpoint of the termination of the desired movement between them.

A more specific object is to provide an improved lock for securing thegimbals of a large telescope together in order to prevent unauthorizeduse.

A more general object is to provide in a telescope mount a provision forremotely locking, unlocking and relocking two sets of gimbals to eachother in the minimum of time with a high degree of accuracy and in whichthe lock is to uncouple from the mating gimbal in such a manner that themotion of the gimbals is unaffected by the presence of the lock.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of atypical telescope and mounting of the larger type and to which theimproved lock structure is applied as an accessory. The lock structureis shown in section.

FIG. 2 represents a section of the lock structure taken on line 2-2 inFIG. 1 and looking in the direction of the arrow.

FIG. 3 is an end view of the lock structure, taken at about line 2-2 inFIG. 1 and showing the lock members in an unlocked position, i.e., theelevation or quadrilateral gimbal is free to swing, either by power orby hand. The figure is drawn to about twice the size of FIG. 1.

FIG. 4 is a view similar to FIG. 3 but in which the lock members havemade contact with a stationary ring surface attached to the yoke or forkgimbal.

FIG. 5 depicts a section taken along line 5-5 in FIG. 3.

FIG. 6 is an enlarged schematic view of a single unit of the lockmechanism and showing the placement of the pivot points of the lock.

FIG. 7 shows a circuit controllable from the eyepiece switchboard forenergizing an improved two-part solenoid which operates the pump.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing to the left of FIG.1 shows a typical large telescope of the so-called two gimbal" type andto which the improved locking assembly or accessory shown to the rightof FIG. 1 is particularly useful. Reference character I designated ingeneral the fork or yoke gimbal of a large telescope mount. This gimbalis provided with a pair of oppositely positioned legs 2 joined togetherby a large casting 3 which fits around a shaft 4. The casting 3 hasgenerally a rectangular cross section and is hollow over at least someportion thereof in order to reduce the weight as much as possible. Thecasting is keyed to the shaft 4 as indicated at 5. The shaft 4 restsupon, and is secured to, a heavy metal plate 6, the lower surface ofwhich formspart of the race of a ball bearing 7 of which the other raceportion is contained in a large and fairly heavy baseplate 8. A drivingshaft 9 extends upwardly through an opening in the base plate and isconnected to the circular plate 6. This shaft carries at the lower end alarge gear 10 which meshes with a small gear 11, the latter beingcarried on a shaft 12 which mechanically connects with a motor 13. Theshaft 9, gears 10, 11, the motor shaft the motor 13 are contained in awell 14 formed in a concrete floor, the plate 8 being sufficiently largeto extend over the well and is secured to the floor.

Each of the legs 2 near the top is provided with openings which carryball bearings 15 and the latter rotatably support a shaft 16. Each shaftextends inwardly into the space between the legs 2 and are fixedlymounted in a pair of heavy anchoring devices 17 which are bolted orotherwise secured to the upper or elevation gimbal 18. The latter has aquadrilateral shape (not shown) and a square cross section of wide andthick dimensions and is cast with a hollow space which extends aroundthe four lengths of the gimbal. These lengths are spaced a considerabledistance apart and within this space there are a number of struts orbraces extending inwardly (not shown) which support a large circularmetal casting 19 closed at the bottom but open at the top. A metalfrustum of a cone 20, forming a shield, extends upwardly from the openor upper edge of the casting 19, the latter serving as a lower supportfor a number of struts or rods 21 forming a framework which supports atthe top a disc member 22. This member has a central opening forreceiving a metal cylinder 23 which contains a condensing lens (notshown) of any-suitable and well-known type. The distance between thelens at the top and the gimbal 18 could be quite considerable in thecase of a large telescope installation. Within the circular casting 19there are wellknown supports (not shown) for locating a large reflectinglens 23' which focuses the rays onto the deflecting mirror 24 and theserays then enter the lens system of the eyepiece at the observer station.The observer in looking through the eyepiece under focus can direct thesmall condensing lens at the top of the framework onto the star,satellite or any other object assuming that he has been able to swingthe elevating gimbal about its shaft 16, and also the fork gimbal 1about its vertical bearing. The manner in which this is accomplishedwill be described in greater detail hereinafter. To the right of theobservers station or eyepiece there is a platform having a number ofpushbuttons 26, as will also be explained hereinafter, for controllingthe movement of the two gimbals and also for other purposes. Theright-hand shaft 16 carries a disc 27 and a corresponding disc or plate28 is mounted on the heavy plate 6, these discs having angular markingsthereon so that the observer would know the angular displacement of thegimbals as they are swung in their respective directions. In order toswing the gimbal 18 so as to elevate or depress the telescope, there isloosely carried on the left-hand shaft 16, a large gear 29 which mesheswith a small gear 30. The latter is connected either directly to themotor 31 through a shaft 32 or through a suitable form of declutchingmechanism which can be remotely controlled by an electrical impulse asexplained hereinafter. This declutching mechanism is indicated simply asa small rectangle 33. The motor 31 is suspended from the lower surfaceof the gimbal 18 in any suitable manner, and circuits (not shown) areconnected between each of the motors 31 and 13 to the push button group26 located on a keyboard in easy reach of the observer.

IMPROVED LOCK STRUCTURE The lock structure assembly constituting ourinvention takes the form of an accessory generally designated at 33'.However, the structure of the accessory about to be described could beconcealed within the telescope mount itself and not project beyond oneof the legs of the fork gimbal. There is a hub member 34 of roundconfiguration having a flange 35 which is bolted to one of the legs ofthe fork gimbal and in line with an extension of shaft 16. A web 36 ofsubstantial thickness extends radially outward from the hub member 34and this web carries an overhanging ring member 37 which is also ofconsiderable thickness. The member 37 has an inside peripheral surface38 which is preferably ground to a perfectly round configuration. Thering surface 38 maintains a rigid position in space but moves with thefork gimbal. Within the hub member 34, there is a cylinder 39 ofsubstantial thickness which runs free of the hub member and is attachedto the shaft by a holding nut 40. The cylinder is supported peripherallyon ball bearings 41 and is driven by the shaft 16. Thus, as theelevation gimbal 18 swings on its shafts 16 the cylinder 39 turns freelyin the same amount within the surrounding metal housing. The cylinderhas an extended portion 42 of smaller diameter than the main portion andis closed at the remote end as indicated at 43. This cylindrical portioncontains a piston 44 having a piston rod 45 which is extended to theleft (as seen in FIG. 1) to form the core of two adjacently posi tionedbut separately operated solenoids 46, 47. The separation of thesesolenoids are indicated by the line 47' and the purpose of separatingthem will be explained hereinafter. It is apparent that when either ofthe solenoids 46, 47 or both are electrically energized, the core withinthe solenoid which represents the extension of the piston rod 45 willmove the piston 44 to the right. The maximum travel of the piston issuch that a small space is still left between the end of the piston andthe end 43 of the cylinder. The cylinder portion 42 is provided withfour quadrantally arranged segments 48, which extend outwardly edgewisefrom the cylinder to which they are secured. These segments aresubstantially pie-shaped with a round outer periphery and terminate ateach end in flat, smooth edges, the adjacently positioned edgesconstituting pairs and positioned at right angles to one another so thatthe assembly of these segments present four grooves 48 having parallelsides and extending radially outward from the center of the segmentassembly.

Projecting from each side of the segmental surfaces, as seen in FIG. 1,and formed integrally therewith there is a pair of projections or lugs49 which have flat surfaces and are separated from the segmentalsurfaces by a space indicated at 50. Thus, the projections or lugs 49extend on both sides of the segmental member assembly, eachcorresponding projection on opposite sides of the segment member beingin line with one another to constitute a pair and in effect extend thegrooves 48' beyond the perimeter of the segment assembly. There is anaperture in each of the projections, the aperture in one projectionbeing in line'with the aperture in the companion projection. Theseapertures receive a pin 52 as seen more clearly in FIG. 1, and thepurpose of which will be explained hereinafter. Each lock member 53 hasa shape similar to that shown in enlarged diagram FIG. 6 and is providedwith an aperture to loosely receive the pin 52. The shape of the lockmember is characterized by a curved surface 54 having the approximatecurvature of the surface 38 formed on the overhanging member 37. Thesides or edges 55, 56 of the member are parallel and the edge 55 islonger than the edge 56. These two edges are closed by the roundedportion 57 and a longer portion 58. The longer edge portion extends atan angle of about 50 with respect to a reference horizontal line and isso illustrated in the figure. Thus, each lock member takes on thegeneral appearance of a triangle with the pivot pin 52 located near thenarrow end of the member. The thickness of the lock member is such as tobe readily slidable between each pair of projections 49. The size of theaperture is such as to permit the member to turn or swing easily on thepin 52 with the pointed end resting on the periphery of the segmentalassembly 48. When mounted in position, the uppermost surface ispositioned somewhat above the lugs 49 as can be seen in FIG. 2. There isa small gap between the upper surface 54 of each lock member and thesurface 38 of the overhanging metal portion 37 (FIG. 2). A secondaperture 58' is provided in the lock member, this aperture beingpositioned near the curved surface 54 and the short edge 56; the purposeof this aperture will be explained hereinafter. Directly over thegrooves 48 and at each side of the segmental assembly, there is a plate59 (FIG. 5) of rectangular shape except having the inner comers cut off.These plates are screwed as indicated at 60 to the outer surfaces of theprojections 49. Thus, a squareshaped compartment 61 is formed (FIG. 5)of which the vertical sides are constituted of the inside edges of thelugs 49 and the top and bottom sides are constituted of the plate 59.Each compartment is closed at the inner end by a disc 62 of metal in anysuitable manner and fastened to the wall of the compartment 61. Withineach compartment there is positioned a bellows device 63 of any suitabletype having a diametrical size as to fit slidably but not loosely withinthe compartment 61. The outer end of each bellows is preferably providedwith a rounded head member 65 of solid metal and the overall length ofthe bellows including the solid head is such that when the inner ends ofthe bellows rest upon the metal disc 62 the solid head member will justcontact the angular surface of the lock member as can be seen in FIG. 6.The disc 62 has an opening therein (not shown) in the center whichcommunicates with the interior of the bellows and also by a suitableconduit system (not shown) with the interior of the cylinder portion 41.it is apparent that when oil is introduced in the space between thepiston 44 and the end 43 of the cylinder and assuming that one or bothof the solenoids 46, 47 are energized and the piston is caused to moveto the right as seen in FIG. 1, the oil is placed under pressure and isforced through the conduit system simultaneously into each of thebellows 63. Thus, the oil under pressure will cause these bellows toelongate outwardly within the compartment 61 causing the edge 58 of thelock member to move outwardly since the disc 62 will prevent movement ofthe bellows inwardly. The head member 65 will press against the surface48 and will cause the lock member to rotate about its pin 52 until thecurved surface 54 makes firm contact with the inside surface 38 of thelocking ring surface. This condition is shown in H0. 4. It will be notedin this respect that the pivot pin 52 is located eccentrically withrespect to the lock member 53 so that an outward pressure exerted on thesurface 38 by the head of each of the bellows provides an enormousleverage in the pressing force available between the head 65' and thesurface 38. Since all of the bellows receive the same oil pressure thesolid head members 65 will exercise equal forces on all of the lockmembers 53 which serve to swing each member about its pin 52. The longcurved surface 54 provides an enormous length of contact at each of thefour positions about the segmental assembly 48, each position beingrepresented by two lock members actuated by the end 65 of the individualbellows. Due to the rigidity of the ring member 37, these pressures aredistributed almost equally about the entire cylindrical body of themember. This force reacts through the shaft 16 on the elevation gimball8 and stops the latter immediately at the farthest position of thepiston when the solenoids 46, 47, or either one of them, are energized.

The energization of the solenoids is preferably controlled by one ormore of the keys 26 located at theobservers post. A suitable form ofelectrical circuit that may be employed for this purpose is illustratedin FIG. 7 and will be described hereinafter. When it is desired to swingthe elevation gimbal to a new position of the telescope, the solenoidsare first deenergized and the lock members 53 are caused to withdrawfrom the surface 38 by means of a return spring 67 which loosely fitsinto an aperture 58' in the lock member and is bent to clear the outersurfaces of the lugs or projections 49. The other end of the spring isfrictionally held under a small triangularly shaped plate 68, riveted orotherwise secured to the outside surfaces of the segmental assembly.These springs must assert sufficient force to swing each lock memberabout its pin and thus return the member to its original position. Theoil passes through the conduits (not shown) under spring pressure to thespace within the cylinder so as to move the piston to its original orleft-hand position. The elevation gimbal is then allowed to freely swingon its axis and driven, if desired, by the motor 31 until a fix has beenmade at the lens 23 on the desired star at which time the observersimply presses the stop button at the keyboard and an abrupt stoppageagainst further movement of the gimbal is again effected. On theenergization of the solenoids 46, 47 in the manner described, it may bedesirable to provide a declutching mechanism between the gear 30 and themotor 31 which may be of any suitable and well-known type, such as todisconnect the motor 31 upon the energization of the solenoids 46, 47.The declutching effect may also be exercised by a suitable push button26. It will be noted that the stop or braking effect exercisedhydraulically by the bellows 63 is independent of any horizontalmovement of the fork gimbal 1 since the abrupt stoppage of movementreacts only on the shafts 16 of the elevation gimbal and not on theshaft 4 of the fork gimbal. Thus, the overhanging metal portion 37, andparticularly the inner surface 38, constitutes a locking ring which iseffective regardless of the position of the fork gimbal.

A suitable circuit that may be employed for energizing the solenoids 46,47 and controlled by push button is shown in FIG. 7. One end of thesolenoid 47 is connected to a switch 69 and the latter is also connectedto one end of the solenoid 46. The other end of the solenoid isconnected by a conductor to one end of a resistance 70. The opposite endof the resistance is connected to the right-hand end of the solenoid 47and also to one pole of a battery 71. The other side of the battery isconnected both to the left-hand end of the solenoid 47 and also to theswitch 69. A switch 72 is connected across the resistance 70 so as toshort out the latter when desired. The battery 71 may have a voltage ofabout 40 direct current. To move the bellows 63 outwardly, and to applythe maximum force by the core on the piston 44, it is necessary to closeboth switches 69 and 72, in which case battery voltage at full strengthis applied to each of the solenoids 46, 47. However, after the solid tip65 has caused the lock members to contact the locking surface 38, and itis desired that this locking effect should extend over long periods oftime in order to discourage any unauthorized movement of the elevationgimbal 18, it may be desirable to cut the voltage applied to thesolenoid 46 but apply full voltage only to the solenoid 47. In thiscase, the switch 72 is opened, which in effect inserts the resistance inthe circuit which contains the solenoid 46. The resistance 70 issufficiently high that when the battery 71 is assumed to be 40 volts DC,the voltage applied to the solenoid 46 is reduced by dropping 45.5 voltsacross the resistance. The net effect is to reduce the dissipatedwattage from approximately 40 watts to 4 watts and sufficient energywill still be applied to the solenoids 46, 47 to firmly hold the lockmembers 53 tightly against the locking surface. This may save using anexcessive amount of power if it isdesired that the locking effect shouldextend over long periods of time to prevent any unauthorized movement ofthe elevation gimbal.

One advantage, of this hydraulic lock over all other locks, includingthe use of the wedges between machine parts, is that it is capable ofwithstanding the environment, such as vibration, etc., without slippageof the lock. Moreover, the presence of the lock does not apply anystrain about the elevation axis of the telescope mount. Finally, thehydraulic system is effective, regardless of the relative positions ofthe fork gimbal and the elevation gimbal. It is also apparent that sincethe oil pressure is obtained from the centrally located piston 44, thispressure is applied to all of the bellows 63 simultaneously and in equalamounts. Thus, the force exercised by the lock members 53 against thelocking surface 38 is equally distributed about the surface of thelocking ring to provide the optimum locking effect and thus prevent eventhe slightest tendency for the elevation gimbal l8to overrun its properposition, as determined by the observer.

We claim:

1. In a telescope mounting including a pair of gimbals swivellyconnected together for permitting the telescope to be moved in thevertical and horizontal directions, the vertical moving gimbal beingsupported on oppositely positioned shafts journaled on a horizontallymoving gimbal, and. brake means attached to said extended shaft forapplying a braking effect to the swinging movement of the gimbal whichpositions the telescope in the vertical direction said brake meanscomprises a cylinder secured to the periphery of the cylinder andextending radially outward, the edge portions of the plate sectionsbeing spaced from one another to form outwardly extending slots whichhave parallel sides and the slots being arranged at right angles to oneanother, expandable elements in said slots, said elements terminating insolid heads at their outer ends, said elements being responsive tohydraulic pressure in order to expand, a pair of lock members swingablymounted on pivots on opposite sides of each slot, said members havingtapered edges which bear against the head of said expandable elements,the lower end of the member bearing against the periphery of themultisection plate member, a stationary ring member surrounding saidexpansible elements, and means for causing each cxpansible element toelongate and swing the lock members about their respective pivots tomake contact with the stationary ring member when hydraulic v pressureis applied to each element whereby a braking action is effected on theelevation moving gimbal through said cylinder and shaft extension toprevent overrun of one gimbal with respect to the other gimbal.

2. In a telescope mounting according to claim 2 and in which saidelements consist of bellow members closed at the head end and incommunication at the other end with the hydraulic pressure developedwithin said cylinder.

3. In a telescope mounting according to claim 2 and in which thehydraulic pressure is developed by a solenoid and piston structurecontained within said cylinder and controllable from the eyepieceposition.

4. In a telescopic mounting according to claim 2 and in which said lastmentioned means includes a cylinder, a piston within the cylinder and asolenoid in the cylinder having a core connected to said piston, saidsolenoid being electrically controllable from the observers position,oil in the cylinder at the position of the piston which upon thecompression stroke of the piston forces the oil into the expansiblemembers which serve to press the lock members against said lockingsurface.

5. In a telescope mounting according to claim 1, said means for causingeach expansible element to elongate being constituted of a solenoid insaid cylinder, a core in said solenoid and connected to a piston locatedat one end of the cylinder, the piston end of the cylinder being incommunication with said expansible elements, oil in said cylinder sothat when the solenoid is activated, the piston moves to place the oilunder pressure which is forced into the expansible elements, astationary ring surrounding the expansible elements and secured to thehorizontally moving gimbal, said expansible elements upon receiving theoil under pressure expands and contacts the stationary ring wherebyapowerful braking action is obtained and the gimbal which moves thetelescope in the vertical direction is brought to a complete stop toprevent overrun.

6. In a telescope mounting according to claim 1, a locking gimbal formaintaining the telescope at a desired position in elevation, saidgimbal including a bearing structure for receiving a shaft on which thetelescope can move in the vertical direction, said structure alsoincluding a metal ring which is secured to the gimbal that moves in thehorizontal direction and having an interior peripheral surface whichconstitutes a locking surface, a plurality of lock members formaintaining the telescope and its bearing structure fixed with respectto the horizontally movable gimbal, and means for hydraulically pressingthe lock members against the locking surface when the telescope ispointed at the precise altitude of the target star.

7. In a telescope mounting according to claim 3 and having spring meansoperable on the withdrawal of the hydraulic pressure for removing thelock members out of contact with the locking ring so as to permit thetelescope to be moved in elevation.

8. ,In a telescope mounting according to claim 3 and in which said ringincludes a casting which surrounds at least one end of said cylinder andis connected to the gimbal which moves in the horizontal direction, saidcasting having a radially extending web which carries an annular memberof substantial thickness and extends in the horizontal direction, theinside surface of said annular member presenting a cylindrical surfaceagainst which said lock can contact when hydraulic pressure is appliedto the expansible element.

1. In a telescope mounting including a pair of gimbals swivellyconnected together for permitting the telescope to be moved in thevertical and horizontal directions, the vertical moving gimbal beingsupported on oppositely positioned shafts journaled on a horizontallymoving gimbal, and brake means attached to said extended shaft forapplying a braking effect to the swinging movement of the gimbal whichpositions the telescope in the vertical direction said brake meanscomprises a cylinder secured to the periphery of the cylinder andextending radially outward, the edge portions of the plate sectionsbeing spaced from one another to form outwardly extending slots whichhave parallel sides and the slots being arranged at right angles to oneanother, expandable elements in said slots, said elements terminating insolid heads at their outer ends, said elements being responsive tohydraulic pressure in order to expand, a pair of lock members swingablymounted on pivots on opposite sides of each slot, said members havingtapered edges which bear against the head of said expandable elements,the lower end of the member bearing against the periphery of themultisection plate member, a stationary ring member surrounding saidexpansible elements, and means for causing each expansible element toelongate and swing the lock members about their respective pivots tomake contact with the stationary ring member when hydraulic pressure isapplied to each element whereby a braking action is effected on theelevation moving gimbal through said cylinder and shaft extension toprevent overrun of one gimbal with respect to the other gimbal.
 2. In atelescope mounting according to claim 2 and in which said elementsconsist of bellow members closed at the head end and in communication atthe other end with the hydraulic pressure developed within saidcylinder.
 3. In a telescope mounting according to claim 2 and in whichthe hydraulic pressure is developed by a solenoid and piston structurecontained within said cylinder and controllable from the eyepieceposition.
 4. In a telescopic mounting according to claim 2 and in whichsaid last mentioned means includes a cylinder, a piston within thecylinder and a solenoid in the cylinder having a core connected to saidpiston, said solenoid being electrically controllable from theobserver''s position, oil in The cylinder at the position of the pistonwhich upon the compression stroke of the piston forces the oil into theexpansible members which serve to press the lock members against saidlocking surface.
 5. In a telescope mounting according to claim 1, saidmeans for causing each expansible element to elongate being constitutedof a solenoid in said cylinder, a core in said solenoid and connected toa piston located at one end of the cylinder, the piston end of thecylinder being in communication with said expansible elements, oil insaid cylinder so that when the solenoid is activated, the piston movesto place the oil under pressure which is forced into the expansibleelements, a stationary ring surrounding the expansible elements andsecured to the horizontally moving gimbal, said expansible elements uponreceiving the oil under pressure expands and contacts the stationaryring whereby a powerful braking action is obtained and the gimbal whichmoves the telescope in the vertical direction is brought to a completestop to prevent overrun.
 6. In a telescope mounting according to claim1, a locking gimbal for maintaining the telescope at a desired positionin elevation, said gimbal including a bearing structure for receiving ashaft on which the telescope can move in the vertical direction, saidstructure also including a metal ring which is secured to the gimbalthat moves in the horizontal direction and having an interior peripheralsurface which constitutes a locking surface, a plurality of lock membersfor maintaining the telescope and its bearing structure fixed withrespect to the horizontally movable gimbal, and means for hydraulicallypressing the lock members against the locking surface when the telescopeis pointed at the precise altitude of the target star.
 7. In a telescopemounting according to claim 3 and having spring means operable on thewithdrawal of the hydraulic pressure for removing the lock members outof contact with the locking ring so as to permit the telescope to bemoved in elevation.
 8. In a telescope mounting according to claim 3 andin which said ring includes a casting which surrounds at least one endof said cylinder and is connected to the gimbal which moves in thehorizontal direction, said casting having a radially extending web whichcarries an annular member of substantial thickness and extends in thehorizontal direction, the inside surface of said annular memberpresenting a cylindrical surface against which said lock can contactwhen hydraulic pressure is applied to the expansible element.